Best thing to do is sign up for a distance learning course (I used CATS because they were the cheapest at the time) It'll be about $3000 plus $100 per exam. You can take as many exams as you like in a 'sitting' (4 day period twice a month) but you only get 6 sittings in an 18 month window. You can't just study then test one at a time. Many do two sittings of 7 exams each, others 5/5/4. I did 4/4/3/3 as I find it easier to study fewer subjects in bite sizes chunks.
You're looking at about a year for the theory. I wouldn't even think about finding somewhere to actually fly until you've got 14 passes. You might decide you have better things to do.
With your flight time - From memory the minimums are 7 hours to convert a CPL and 15 hours to convert an IR. You can convert an FAA ATP to a Frozen ATPL (CPL/IR with ATPL theory credits), but in Europe an ATPL actually means something - you can't get one in a cessna like back home - you need 500 hours multi crew. If by chance you have 500 hours multi crew, you can convert ATP > ATPL but you'll need to google that one for yourself.
Either way, get started on those 14 horrendous exams. You'll need to know who attended the Convention of Chicago, who sat where, who walked their dog and what they had for breakfast. You'll need to know about GPS: Satellite orbits, heights, slant angles, frequencies, atomic clock accuracies, azimuth angles etc - just not how to turn it on and use it. You'll need to know the local name of a wind that blows down just one valley on the other side of the planet, and the prevailing winds at any point of the globe at any given time of year.
In short, you'll love it!!